Combine butter or margarine and mints in a 2-cup glass measure; microwave at high for 30 seconds or until soft. Stir until smooth and set aside to cool.

Lightly spoon flour into a measuring cup and level with knife. Combine flour, baking soda and salt in a bowl.

Combine sugar, cocoa, egg and egg white in a large bowl. Beat at medium speed with mixer until well-blended. Add mint mixture and beat well. Add flour mixture; beat at low speed just until blended.

Pour batter into prepared pan. Bake for 20 minutes or until a toothpick inserted in center comes out clean. Cool completely on wire rack.

Poster's Notes:
These are cake-y, rather than fudgy, brownies. I think adding some chopped chocolate, chocolate chips, or even some additional chocolate-covered mints cut into small pieces, would make them even better.